Kingley
1148 posts
May 10, 2010
11:43 AM
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I have been wiring a volume control into a bullet mic and have encountered a problem. The pot doesn't have a full gradual volume sweep as it should, but is acting more like an on/off switch. It takes less than a quarter turn for the volume to reach maximum.
I have wired it up so that the wire from the screw on connector is going to the middle pin of the pot. Then the negative and positive wires from the element go to the pins on either side of the pot. I also have a ground going from the element to the mic shell.
As far as I'm aware the pot is a 250K linear potentiometer (it was given to me and that's what the guy said it was).
Any suggestions as to what I have done wrong and why the pot is not working as a full gradual volume sweep as it should?
I appreciate any help you guys can offer.
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Harpaholic
83 posts
May 10, 2010
12:05 PM
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I don't ground the element to the shell, not to say you can't.
Your using the proper lugs, but I think you problem is you didn't ground the pot, but I may be wrong?
I run a wire from the ground lug of the pot to the bottom of the pot (flat side) and solder the wire to it. That is also the same lug I use for the element ground. Once I mount the pot, it's becomes the common ground to the shell.
You don't have to do it that way, but you need to ground the pot to the shell somehow.
If not, the pot is bad?
Last Edited by on May 10, 2010 12:10 PM
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Kingley
1149 posts
May 10, 2010
12:23 PM
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Sorry for the confusion. I got it wrong. I ran the ground from the negative of the pot to the shell, not from the element.
My current thoughts are either the pot is an audio taper and not linear, or it's bad as you suggest Harpoholic.
I guess I'll have to get a new pot and fit it, unless anyone has any other thoughts/ideas.
Last Edited by on May 10, 2010 12:24 PM
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barbequebob
809 posts
May 10, 2010
12:27 PM
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If it acts more like a glorified on/off switch, it could be an audio taper, but IMO, more likely it could be an impedance mismatch with the cartridge you've got in the mic. As an example, a 5meg pot is great for crystal/ceramic mics, but with a CM/CR mic, that impedance is too high and winds up acting like an on/off switch because CM/CR mics are a much lower impedance.
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Sincerely,
Barbeque Bob Maglinte
Boston, MA
http://www.barbequebob.com
CD available at http://www.cdbaby.com/cd/bbmaglinte
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7LimitJI
118 posts
May 10, 2010
12:34 PM
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If you have an ohmeter you could check it with that.
Try swapping the negative lead to the other connection.
This will mean the pot will work in the opposite direction. Clock or anti clockwise.
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Those Dangerous Gentlemens Myspace
Due to cutbacks,the light at the end of the tunnel has been switched off.
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Kingley
1150 posts
May 10, 2010
12:40 PM
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Thanks for the suggestions guys.
BBQ Bob - I suspect you're right. I'll get a new pot.
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arnenym
2 posts
May 10, 2010
12:57 PM
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Hold the pot in front of you with the shaft pointing out With the solder lugs on the upper side you have the incoming signal to right, out in the middle and ground to the left side
The red plus from mic in on the right lug and the mic cable connection in the middle. If you ground the black in the shell you get a protect shield to avoid hum..
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tookatooka
1390 posts
May 10, 2010
1:11 PM
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The pot (potentiometer) has three solder lugs.
The middle lug is the wiper. This is indirectly connected to the spindle of the pot and moves a small metal wiper back and forth over a carbon track which is the resistive element.
The other two solder lugs are connected to either end of the resistive element (the carbon track).
If it's an old pot which you have been given, it may be that the carbon track is cracked. This may be what is causing your problem.
As already mentioned, it can be checked with an ohmeter pretty easily.
Last Edited by on May 10, 2010 1:12 PM
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MJ
164 posts
May 10, 2010
3:24 PM
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I think for a CM element you should be using a 100K pot.
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rharley5652
137 posts
May 10, 2010
3:43 PM
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100K-250K pot audio taper or linear is fine on a CM-CR ,I prefer the linear pots <.
Hold the pot in front of you with the shaft pointing out With the solder lugs on the upper side,..middle lug to amp ,.left lug to + element,.right lug to - element an all grounds,..
bad pot may be what it is ,.make sure it's 100-250K pot.
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Simply Unique Kustom Mic's By Rharley
Last Edited by on May 10, 2010 4:01 PM
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rharley5652
138 posts
May 10, 2010
3:57 PM
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@ Kingley,..if ya hooked up like this ya should be good to go <>
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Simply Unique Kustom Mic's By Rharley
Last Edited by on Jan 09, 2011 12:13 AM
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Greg Heumann
442 posts
May 10, 2010
5:06 PM
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yep, yep and yep. Rharley is right. Either taper should work without the symptom you describe. The shell SHOULD be grounded - it is unavoidable anyway if you're using a screw-on connector. Either bad pot or one of too high a resistance (technically pots are measured by resistance, not impedance - the two are related but not the same thing.)
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/Greg
BlowsMeAway Productions
BlueState - my band
Bluestate on iTunes
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oldwailer
1243 posts
May 10, 2010
7:49 PM
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So--just slightly off topic--but while we're all here on this subject--I have a bullet that I put a pot into--works great--except the damn knob turns backwards to increase the volume. I haven't really been able to get used to it in over a year.
Which leads do I need to reverse to make it work right?
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rharley5652
139 posts
May 11, 2010
10:09 PM
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@oldwailer,..
look at how the outer two wires are soldered an just reverse them ,.should work the way ya want ,.I take it when ya say:
except the damn knob turns backwards to increase the volume.
Ya mean that it's workin counterclockwise <>?
@ Kingley ,..if your volume control has a capacitor on it that may also be your problem,..I ran into this problem once,..put to large of a cap on,. an it was just like a on-off switch,..
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Simply Unique Kustom Mic's By Rharley
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Kingley
1151 posts
May 11, 2010
10:20 PM
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Thanks for the great info guys. Upon investigation it is the wrong value pot. I'll have to get a new pot.
Does anyone know of the best place in the UK to order one from?
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rharley5652
140 posts
May 12, 2010
12:21 AM
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King ,.good to hear ,..any local music shop should have the 100 - 250k pot ya need ,.I myself like the linear pots as audio pot comes on to fast,.. choice is up to ya,..
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Simply Unique Kustom Mic's By Rharley
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barbequebob
812 posts
May 12, 2010
5:52 AM
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Those pots are easy to find because these are commonly used on guitars.
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Sincerely,
Barbeque Bob Maglinte
Boston, MA
http://www.barbequebob.com
CD available at http://www.cdbaby.com/cd/bbmaglinte
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Harpaholic
92 posts
May 12, 2010
8:25 AM
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The audio pots I use have a nice even sweep from 1-10 on a 100k-250k pot.
From Wiki:
Most (cheaper) "audio" pots are actually not logarithmic, but use two regions of different resistance (but constant resistivity) to approximate a logarithmic law.
The 'log pot' is used as the volume control in audio amplifiers, where it is also called an "audio taper pot", because the amplitude response of the human ear is also logarithmic. (not linear) It ensures that, on a volume control marked 0 to 10, for example, a setting of 5 sounds half as loud as a setting of 10
We can go round and round about audio vs linear all day long. I prefer audio pots. Use what you like!
250K audio pots are typically used in Fender guitars with single coil p ups, 500k audio pots are typically used for soapbars, and humbuckers.
Last Edited by on May 12, 2010 8:59 AM
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Kingley
1153 posts
May 12, 2010
9:23 AM
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7LimitJi - Thanks for the link.
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rharley5652
141 posts
May 12, 2010
2:16 PM
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I like 100k for Dynamic ,.250k for CM-CR's,.1meg or more for crystals ,.5 meg being the best if ya can find em <>
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Simply Unique Kustom Mic's By Rharley
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